Numerous industrial processes, especially coal and petroleum combustion, produce exhaust gases containing one or more sulfur oxides. As more such industrial processes are performed, more and more sulfur oxides are being released into the air. Environmental and health concerns have motivated government and industry to reduce the levels of sulfur oxides in exhaust gases.
Chinese patent application CN201010519504.6 describes the Claus process, which recovers elemental sulfur from the gaseous hydrogen sulfide using sequential use of multiple thermal reactors and catalytic condensers.
The limestone-gypsum flue gas desulfurization process involves absorption of sulfur dioxide by limestone. The sulfur dioxide is oxidized by reacting it with air sparged into an absorber-recirculation tank.
As described in Chinese patent document no. 201510009642 and in patent applications nos. PCT/CN2014/087887 and PCT/CN2013/074657, ammonia is an effective desulfurization agent because it is a material that is easy to dissolve in water, is highly reactive with sulfur oxides, and readily produces easy to remove ammonia-sulfur species such as ammonium sulfate. It also produces ammonium sulfite.
Unfortunately, use of ammonia as a desulfurization agent results in additional complexities and difficulties. Because it is so reactive, ammonia can also form other species that exit with the gas in the form of aerosol pollutants. In addition, ammonia readily evaporates into a gas and flows along with the rest of the gas. As a result, ammonia slip is a common problem associated with desulfurization using ammonia.